Figure 1

Computer simulation of the path $\mathit{S}\mathbf{(}\mathit{t}\mathbf{)}$ , $\mathit{I}\mathbf{(}\mathit{t}\mathbf{)}$ , $\mathit{Q}\mathbf{(}\mathit{t}\mathbf{)}$ for model ( 1.3 ) and ( 1.1 ) for parameter values $\mathit{A}\mathbf{=}\mathbf{0.8}$ , $\mathit{\beta }\mathbf{=}\mathbf{0.6}$ , $\mathit{\mu }\mathbf{=}\mathbf{0.4}$ , $\mathit{\alpha }\mathbf{=}\mathbf{0.2}$ , $\mathit{\gamma }\mathbf{=}\mathbf{0.3}$ , $\mathit{\epsilon }\mathbf{=}\mathbf{0.2}$ , $\mathit{\delta }\mathbf{=}\mathbf{0.1}$ and $\mathit{\sigma }\mathbf{=}\mathbf{0.4}$ , with step size $\mathbf{\Delta }\mathit{t}\mathbf{=}\mathbf{0.001}$ and initial value $\mathbf{(}\mathit{S}\mathbf{(}\mathbf{0}\mathbf{)}\mathbf{,}\mathit{I}\mathbf{(}\mathbf{0}\mathbf{)}\mathbf{,}\mathit{Q}\mathbf{(}\mathbf{0}\mathbf{)}\mathbf{)}\mathbf{=}\mathbf{(}\mathbf{0.8}\mathbf{,}\mathbf{0.4}\mathbf{,}\mathbf{0.5}\mathbf{)}$ .